1. Field of the Invention
The present invention relates to a composite light-emitting material and a light-emitting device comprising the same. More particularly, the present invention relates to a composite light-emitting material comprising two or more light-emitting materials of an inorganic phosphor, a semiconductor nanocrystal and an organic dye in which the surfaces of the two or more light-emitting materials are coated, and a light-emitting device comprising the same.
2. Description of the Related Art
Light-emitting materials exhibiting emission properties caused by an energy stimulus have been widely used in display devices such as light source devices, cathode ray tubes, plasma displays or field emission displays, and light-emitting sensors for bio-tagging. There is a need for a light-emitting device to employ a light-emitting material capable of maximizing luminous efficiency and stably maintaining the emission properties. Representative examples of light-emitting materials for a display device include an inorganic phosphor, an organic dye, a semiconductor nanocrystal and the like.
Among them, the semiconductor nanocrystal (“quantum dot”) is prepared by pulverizing a semiconductor compound into a nano-sized crystal, which exhibits a quantum confinement effect in a smaller range than the bulk exciton Bohr radius of the semiconductor compound, thereby leading to a change in band gap energy of the semiconductor compound.
The luminous efficiency of the light-emitting material depends on the surface characteristics such as surface structure, composition, or surface crystallinity of a light-emitting material particle. Since the semiconductor nanocrystal has a relatively large surface area due to its very small size, it is apt to raise any defects on the surface thereof. These defects function as various energy traps in the band gap energy, thereby lowering the luminous efficiency of the semiconductor nanocrystal. Moreover, this phenomenon becomes more serious if semiconductor nanocrystals are combined.
In the case of the inorganic phosphor, its emission property tends to change easily by oxidizing the surface thereof due to the contact with oxygen and moisture. Further, when electrons continuously accumulate on the surface, it is hard to get them to an excitation state owing to the charging thereof, which may lead to the reduction in the luminous efficiency.
Meanwhile, in the case of the organic dye used as a light-emitting material, if it is exposed to excitation light having high energy for a long time, the safety of the material itself is lowered, thereby significantly decreasing the luminous efficiency.
As described above, since the structure of the light-emitting material is affected by the property of the material, environmental conditions, energy excitation state, and the like, its emission properties may be changed or luminous efficiency may be deteriorated. Therefore, a coating method for wrapping a protecting film on the surface of the light-emitting material with a stable organic or inorganic material has been used. Further, methods for coating the surface of a phosphor particle with a protecting material include a sol-gel method, a liquid phase coating method such as an absorption method based on an electrostatic principle in a solution, and the like.
One method includes coating the surface of a semiconductor nanocrystal with a semiconductor compound having high band gap energy.
Hitherto, however, there was no prior art for combining two or more light-emitting materials into a single structure by fusing them so as to improve the luminous efficiency and lifetime of a light-emitting material.